包含硅量子点的富硅SiN_x薄膜结构与发光特性

Photoluminescences and structrue performances of Si-rich silicon nitride thin films containing Si quantum dots

采用等离子体增强化学气相沉积法,以NH3与SiH4为反应气体,n型单晶硅为衬底,低温(220°C)沉积了富硅氮化硅(SiNx)薄膜.在N2氛围中,于500—1100C范围内对样品进行了热退火处理.采用Raman光谱技术分析了薄膜内硅量子点的结晶情况,结果表明,当退火温度低于950°C时,样品的晶化率低于18%,而当退火温度升为1100°C,晶化率增加至53%,说明大部分硅量子点都由非晶态转变为晶态.实验通过Fourier变换红外吸收(FTIR)光谱检测了样品中各键的键合结构演变,发现Si—N键和Si—H键随退火温度升高向高波数方向移动,说明了薄膜内近化学计量比的氮化硅逐渐形成.实验还通过光致发光(PL)光谱分析了各样品的发光特性,发现各样品中均有5个发光峰,讨论了它们的发光来源,结合Raman光谱与FTIR光谱表明波长位于500—560nm的绿光来源于硅量子点,其他峰则来源于薄膜内的缺陷态.研究了硅量子点的分布和尺寸对发光带移动的影响,并根据PL峰位计算了硅量子点的尺寸,其大小为1.6—3nm,具有良好的限域效应.

Silicon-rich silicon nitride （SiNx） thin films are deposited at 220 ℃ on n-type monocrystalline silicon substrates by plasma enhanced chemical vapor deposition using NH3 and Sill4 as the reaction gases. The samples are annealed at temperature in a range of 500-1100 ℃ in N2 atmosphere. We analyze the crystalline states of silicon quantum dots （Si-QDs） and calculate the crystalline ratios of samples under different annealing conditions according to the Raman spectra. The crystalline ratio is less than 18% when the annealing temperature is lower than 950 ~C, when the temperature reaches 1100 ℃, the crystalline ratio is increased to 53%, which indicates that most of the Si-QDs have been converted into crystallines. Fourier transform infrared spectra are measured at room temperature to investigate the evolutions of the bonding structures within the SiNx matrix. We find that the wavelengths of Si-N and Si-H bond shift toward higher wavelength, which manifests the formation of near stoichiometric silicon nitride. Photoluminescence generated from all samples is investigated in detail. We find five luminescence peaks, whose origins are analyzed. We conclude that the obvious green luminescence （centred at 500-550 nm） oringinates from Si-QDs and the others come from different defects in the films. The effects of sizes and distribution of Si-QDs on the shift of the luminescence peak are discussed. We acquire that the sizes of Si-QDs are in a rang from 1.6 nm to 3 nm, which have an obvious confinement effect. These results are useful for fabricating contronllable Si-QDs and achievement of luminescent devices based on Si-QDs.